Re: Special date/cal needs eg. "thrid friday of july"

[Doug Knight <doug.knight@uaf.edu>]

Martin,

This script should give you enough information to figure out how to do what
you want.  It is not intended to be used as written; it doesn't do any
syntax checking.

Throw the script in a file, mark it executable, and pass the date you're
looking, in the same format as third friday of july, on the command line.
(e.g. ./some_file third friday of july)

#!/bin/sh

# Parse input
week=$1
weekday=$2
month=$4
case "$week" in
  [Ff][Ii][Rr][Ss][Tt])
    skip_weeks=0;
    ;;
  [Ss][Ee][Cc][Oo][Nn][Dd])
    skip_weeks=1;
    ;;
  [Tt][Hh][Ii][Rr][Dd])
    skip_weeks=2;
    ;;
  [Ff][Oo][Uu][Rr][Tt][Hh])
    skip_weeks=3;
    ;;
  [Ff][Ii][Ff][Tt][Hh])
    skip_weeks=4;
    ;;
esac

# Convert the weekday to a number ( 1 = Monday, 2 = Tuesday, ... )
weekday_no=$( date -d "$weekday" +%u )

# Qualify the month with a year and a day (the first) for
# illustrative purposes
first_of_month=$( date -I -d "${month} 1" )

# Now that we're done formating the input, these three lines do the
# real work.

# Find the weekday number of the first day of the month
# (again 1 = Monday, ... )
first_weekday_no=$( date -d "${first_of_month} ${skip_weeks} weeks" +%u )

# Do some math; difference between desired weekdays + 7 then mod by 7.
let skip_days=(7+weekday_no-first_weekday_no)%7

# Use date to print the date.  You can format if desired.
date -d "${first_of_month} ${skip_weeks} weeks ${skip_days} days"



Doug Knight


Martin Klier wrote:
> Hi Linux Admins,
> 
> is there a command to get something like "thrid friday of july" or "second 
> wednesday each month"? I crossread the manuals for date and gcal, but it 
> seems to be impossible. Next thing I found was gcal, with 
> "--period-of-fixed-dates", but I have not been able to get useful results, 
> and 
> date -d "35 tuesday" (35th tuesday of a year), but I have not been able to 
> limit it to months nor selecting the year (by the way, I do not need it).
> 
> Has somebody experience with this one, and can you give me a hint where to 
> look, or even an example?
> 
> Thanks a lot in advance,